The only thing I've found is to be genuinely, intensely, passionately into something, to the point that it doesn't matter if you're good or not - you just do it for the love. It's annoying because you don't really get to choose what hobbies etc you do, it's just a matter of trying everything and seeing what sticks, but personally I haven't found any other way. A million things have fallen by the wayside for me, and only writing and drawing remain. I'm a decent writer and a truly terrible artist, and I don't care because it's something I have to do.

Obviously it's worth trying a reward system, but it's never worked for me - I preemptively reward myself for things I don't follow through on so I'm am constantly in reward debt :P